The present invention relates generally to fall protection equipment and more particularly to a shock absorbing lanyard having a fall arrest energy absorber formed integrally therewith.
Under normal working conditions, a worker, when working on a scaffold, catwalk or other locations that are at a relatively high place from where a fall could result in serious injury, will wear some type of safety harness. Typically, the safety harness is attached to a lanyard, which in turn is attached to an anchorage point. Various lanyards have been developed in order to provide the necessary resistance to decelerate a worker""s fall.
One such device is illustrated in U.S. Pat. No. 4,618,026 which shows a shock absorbing lanyard having overlaying or superposed sections of webbing which are stitched together and are pulled over a separating means by a force applied thereto during a fall so that successive portions of the superposed sections are separated thereby generating a counteracting force to a fall.
Another type of shock absorbing lanyard is illustrated in U.S. Pat. No. 4,253,544 wherein a tensile load bearing woven core is surrounded by a jacket. The jacket is longer than the woven core and the excess material is bunched or gathered accordion style at one end of the lanyard. An indicator flag is affixed to the gathered section and is released when a suitable load causes the gathered section to stretch.
It would be desirable, therefore, to have a shock-absorbing lanyard formed integrally from one piece of webbing without a woven core since the woven core reduces the energy-absorbing capacity of the lanyard.
Generally, the present invention provides a shock absorbing lanyard utilizing a one-piece webbing construction wherein partially oriented yarn (xe2x80x9cPOYxe2x80x9d) fibers and high-strength yarn fibers are assembled integrally in a first section and assembled separately in a second section. Preferably, the second section is tubular in shape such that the high-strength yarn fibers form a sheath around a core of POY fibers. It is not necessary for the sheath to totally encapsulate the POY fibers, even though this is a preferred embodiment since it protects the POY fibers from wear and weathering. Moreover, the sheath does not necessarily need to be tubular in shape, but simply any grouping of yarns intended for residual strength once the POY fibers reach their designed elongation. The POY fibers provide an energy-absorbing feature by elongating under force. The POY fibers may be nylon, polyester or polypropylene or the like or any combination thereof. The high-strength yarn fibers may be nylon, polyester or aramid or the like or any combination thereof.
The POY fibers and the high-strength yarn fibers are preferably assembled in the integral first section in a one-piece webbing construction by weaving, knitting, braiding or the like. The integral first section locks in the POY fibers relative to the second section which can elongate under force. The high-strength yarn fibers of the sheath are preferably formed into an abrasion resistant weave. Preferably, a section of the sheath is doubled over on itself about a section of the core in order to accommodate elongation of the POY fibers in the core. Alternatively, the sheath may be bunched or gathered accordion style about the core. Preferably, a rip stitch through both the sheath and core in or beside the overlapped section is used to secure the overlapped section.
The sheath need not be overlapped if the residual strength ends (i.e., the high-strength yarn fibers) are set long in the integral first section with respect to the energy-absorbing ends (i.e., the POY fibers). This can be accomplished by forming loops with the residual strength ends of a woven material such as is found in the pile structure of towels or Velcro fasteners. In a knitted webbing, this can be accomplished by knitting the residual strength ends and inlaying the energy-absorbing ends or knitting them with minimal laps. Finally, a braided structure can be formed without a need for overlapping if the energy-absorbing ends are inserted as a core to a circular braid. One could also insert the energy-absorbing ends as the straight ends of a triaxial braid.
The knitted and braided web constructions provide the advantage of simplifying the lanyard assembly. Not only is the overlap step bypassed, but also material usage per lanyard need not be predetermined. Unfortunately, both of these advantages are accompanied by reduced material performance. Without the overlap step, the snag and abrasion resistance of the webbing is reduced since the residual strength ends are loose within the material. Further, if the webbing is formed with small interlace/non-interlace repeat sections so as to avoid predetermined lanyard sections, the performance the of energy-absorbing ends is reduced. This is due directly to the frequent interlacements, which reduce the peak elongation possible. The interlacements also reduce the material strength, especially in knit structures where there is knotting. Further, as the energy-absorbing ends elongate during deployment, friction at the interlacements encourages premature failure of the ends.
Included with the POY fibers may be some high strength or high modulus yarns to set or help set the activation force of the lanyard. High modulus yarns also help to increase the initial deployment forces by bringing the stress strain response of the lanyard closer to the ideal of a constant force. High initial forces also help reduce the deployment distance of the lanyard, which is generally desirable.
The energy-absorbing ends may be a mixture of many material types with the POY fibers. By blending POY fibers of different stress versus strain responses, an improved lanyard stress versus strain response can be achieved. Elastic may also be used in the energy-absorbing ends in order to minimize lanyard length when under low tension. Further, these energy-absorbing ends may have different lengths in the lanyard. This is another way to improve the lanyard stress versus strain response.
The webbing of the present invention can also be used as a component of a harness, self-retracting lifeline, horizontal lifeline, vertical lifeline, or other fall arrest devices.